Effective Dietary Practices of Active People with Diabetes:
Part 2 (Supplementing with Carbohydrates)
By Sheri Colberg, Ph.D., FACSM
Supplementing with Carbohydrate Before, During, and After Exercise
Carbohydrate supplementation is an effective performance enhancer whether or not you have diabetes. In general, taking in extra carbohydrate is not usually necessary for events lasting an hour or less, if you start with normal muscle and liver glycogen stores and moderately low levels of insulin.
But you may need to take in carbohydrate for exercise lasting less than an hour, depending on how much insulin is in your system and whether your blood glucose is likely to drop during the event. If you’re running low on glycogen for any reason or your insulin levels are too high, your muscles will use more of your blood glucose than normal, and you’ll likely have to supplement then as well.
If you train on a regular basis, you will need to take in enough carbohydrate every day to restore your muscle and liver glycogen levels between workouts. The time when your body restores glycogen most rapidly is during the first 30 to 120 minutes after exercise. If you want to minimize your risk of later-onset lows, take in some carbohydrate and keep your blood sugars under control during this time to optimize its repletion. When you have diabetes, you have to be especially careful to keep your blood sugars in control before and after exercise so that your glycogen repletion takes place normally. Your body needs adequate insulin levels, especially more than an hour after exercise when glucose uptake into your cells becomes more dependent on insulin.
Taking in some carbohydrate immediately after you finish a workout or race will speed up your initial glycogen replacement and help lower your risk of developing low blood sugars later, all with minimal need for insulin during that period. Carbohydrate intake also helps ensure that your glycogen stores are maximally loaded by the time your next workout rolls around. Keep in mind, though, that glycogen repletion can take 24 to 48 hours, and you need to control your blood sugars well during that time for maximal carbohydrate replacement. If you eat a low-carbohydrate diet, full restoration of glycogen will take longer; you may want to consider taking in more carbohydrate of any GI (glycemic index) than your normal during that time (at least 100 grams per day) and taking enough insulin (if you use it) to facilitate the storage of carbohydrate as glycogen in your muscles and liver.
Particularly during longer workouts or a long sports event, carbohydrate supplementation benefits all athletes. During marathons or triathlons, extra carbohydrate helps maintain your blood sugar levels, enabling you to keep going at a faster pace for longer without fatiguing. Supplementing even works for intermittent, prolonged, high-intensity sports like soccer, field hockey, and tennis. Always take in adequate carbohydrate, along with sufficient (albeit likely reduced) insulin before, during, and after prolonged moderate- or high-intensity workouts to maintain and restore your muscle and liver glycogen and blood glucose, especially during that window of opportunity for glycogen repletion right after you finish exercising. If your blood sugars are normal or slightly low before exercise, you may also want to take in 10 to 15 grams of moderate- or high-GI carbohydrate without any insulin coverage right when you start, especially if your blood glucose levels typically start to drop during the first 30 minutes of an activity.
Glycemic Effect of Various Carbohydrates
The current dietary recommendations are that 45 to 65 percent of daily calories should be from carbohydrate intake. Whether you eat that amount, more, or less, it is helpful to pay attention to the types of carbohydrate that you’re eating when it comes to treating or preventing hypoglycemia, restoring muscle glycogen, keeping your insulin action high, and optimizing your sport performance.
Carbohydrate with a higher GI, by definition, is absorbed more rapidly and has a more immediate effect on your blood sugars. If you’re treating hypoglycemia, you need to take in a higher-GI carbohydrate source, such as glucose tablets or gels, regular soda, sports drinks, skim milk, hard candies, and even bagels, bread, crackers, cornflakes, and white potatoes. If you develop low blood sugars during exercise, one of these sources will treat it most rapidly, and you can use them to raise your blood sugars at the start of your exercise. Traditionally, people have used orange and other juices to treat lows, but they really aren’t the fastest thing to use because most juices have only a low or moderate glycemic effect.
Glucose tablets or gels have some benefits for treating lows that other substances don’t have. For starters, glucose is the sugar that ends up in your bloodstream most rapidly and abundantly, and it is the primary fuel for your brain and nerves. By way of comparison, other simple sugars, such as fructose, found in fruit, have to be converted into glucose and, therefore, have a lower GI value and a slower effect. Another benefit is that glucose comes in precisely measured amounts—usually 4 grams of glucose per tablet or 15 grams per gel—so you can consume a specific number of grams of rapid-acting carbohydrate without overdoing it. With a little practice, you can easily determine how much each 4-gram glucose tablet or 15-gram gel is likely to raise your blood glucose level under different circumstances.
What you treat yourself with may need to vary by situation. If you’re only slightly low, you may just need a glucose tablet or two. If you’re low and likely to keep dropping from whatever insulin you have on board, then you may need to take in some food or a drink with greater staying power, something with some fat or protein to go with the carbohydrate, like peanut butter crackers or Balance Bars. Milk is a good treatment option for that reason, because it contains seven to eight grams of protein, along with some fat depending on what type (e.g., whole, 2 percent, skim, or others) you are drinking. Skim milk works well, but at least one study showed that for prevention of later-onset hypoglycemia following exercise, whole milk is much more effective than skim or even sports drinks, likely because of the extra fat in the whole variety that takes longer to metabolize. Regardless, during exercise you will likely need high-GI carbohydrates for optimal treatment and prevention of hypoglycemia. When optimizing your blood sugar control after workouts and restoring glycogen, however, you can use carbohydrate-rich foods with varying GI values.
This column is excerpted from Diabetic Athlete’s Handbook (released November 2008 from Human Kinetics), which contains essential exercise-related information and examples for Type 1, Type 1.5, and Type 2 diabetic exercisers. More information is available at www.shericolberg.com.